As is well known in the art, certain silicone oils have considerable antifoaming properties, and such silicone oils are widely used in a variety of environments to control foaming, particularly, of water containing fluids. As an example thereof, silicone oils are used as an antifoaming agent in various apparatus for transporting and cleansing blood. Blood has a high tendency to foam, and any foaming of the blood in such transport and cleansing apparatus considerably disrupts the intended procedures and can cause considerable difficulty when the blood is, even in a lightly-foamed form, again transfused to a patient, for example, in an open heart surgery operation. Foaming of the blood must be reduced or prevented, since foamed blood is life threatening, i.e. can cause air emboli. As another example, silicone oils are used as defoamers in various textile dying processes, where the presence of foamed dye solutions causes non-uniform dying of textiles. Likewise, silicone oils are used in paper-making processes, where, again, foaming causes discontinuity in the paper made by those processes.
Most antifoam silicone oils are not water soluble. While some of the oils are somewhat soluble in very special organic solvents, those solvents do not provide practical solutions of the silicone oils, especially bearing in mind certain properties of those solvents, such as cost, environmental concerns and toxicity. Accordingly, the silicone oils are usually applied in the form of a dispersion, i.e. usually an aqueous and less usually a non-aqueous dispersion. Due to the difficulties of dispersing these silicone oils as an aqueous dispersion, most often, the aqueous dispersions must contain dispersal ingredients which render such aqueous dispersions unsuitable for many applications. For example, a conventional polymeric medical antifoam element is prepared by disposing the silicone oil on a solid substrate form of a polymer. That element may be used in transfer and cleansing devices to prevent foaming of blood. However, medical elements of that nature cannot include any dispersal ingredients which are either harmful to the blood or to the patient, since any such medical element may retain at least some of the dispersal ingredients, and those ingredients can be transferred to the blood.
The general approach in the art for applying such antifoam silicone oils to such medical elements is that of preparing a dispersion of the silicone oil in a fugitive dispersing medium. For example, a dispersion of antifoam silicone oil can be made in trichlorotrifluoroethane (TTE) simply by agitating a mixture of the TTE and silicone oil. A porous polymeric substrate, for example, a polyurethane foam substrate, can then be dipped into that dispersion, and, after removal thereof, the fugitive TTE quickly evaporates from the substrate, leaving only the dispersed silicone oil. This approach, therefore, avoids any possibility of deleterious ingredients remaining in the substrate, and that substrate is, accordingly, quite useful as a medical element for antifoaming in a variety of blood-handling apparatus.
However, regulations now in effect in the United States severely limit the use of chlorinated fluorocarbons, including TTE, and in about 1995 the use of such chlorinated fluorocarbons will be virtually eliminated by those regulations, in order to prevent further ecological damage, i.e. ozone depletion. Therefore, that approach for producing such antifoam substrates will be essentially eliminated by that date. Fugitive dispersing mediums, other than chlorinated fluorocarbons, which have the prerequisite requirements of lack of environmental concerns, toxicity, flammability and the like, are not known. In view thereof, the art has sought other dispersing mediums for the silicone oils.
In this latter regard, a number of different dispersions of silicone oil were previously known in the art. For example, it is known that a siloxane antifoam aqueous emulsion can be prepared with emulsifying agents such as stearyl tartrate, glycerol esters, sorbitan esters of fatty acids, propylene glycol esters, and the like. Since these emulsifiers are food grade emulsifiers, they may be used in human consumable compositions. However, some of these emulsifying agents lead to emulsions of very poor stability and other of the emulsifying agents considerably reduce the antifoaming properties of the dispersion, since these emulsifying agents are foaming agents in themselves. Combinations and variations of such emulsifiers have also been proposed in the art, and U.S. Pat. No. 3,423,340 proposes an aqueous dispersions of a particular siloxane, i.e. benzene-soluble dimethylpolysiloxane and a combination of sorbitan polyoxyethylene monostearate and sorbitan monostearate and/or glycerol monostearate. The emulsion can be further stabilized with thickeners, such as sodium carboxymethyl cellulose.
While such dispersions are acceptable for food compositions which are to be ingested into the body via the alimentary canal, the presence of substantial amounts of emulsifying agents in human blood could cause considerable difficulties, since most emulsifying agents cause substantial damage to blood cells, i.e. hemolysis, and can, therefore, be considered as toxic. Accordingly, compositions, such as the foregoing, cannot be used in producing medical antifoaming elements, as described above.
Somewhat similarly, U.S. Pat. No. 3,650,979 proposed an aqueous dispersion of particular organopolysiloxanes with polyglycol ether or a fatty acid ester thereof or alkyl- or aryl-sulfate or -sulfonate. However, again, these dispersions must include emulsifiers and are not acceptable for the same reasons as in connection with the above-described patent.
Somewhat similarly, U.S. Pat. No. 4,436,647 proposes an emulsion of a very specific organopolysiloxane and a long chain sulfonate ester, such as the sodium salt of stearoyl isethionic acid, thickened with a thickening agent, such as sodium carboxymethyl cellulose, but this composition again, requires substantial amounts of an emulsifier, which renders the composition unsuitable for use in medical antifoam elements.
Other variations of like type emulsions have been described in U.S. Pat. Nos. 3,666,681 and 4,225,456, but, here again, each of these are not suitable for use in medical elements.
Finally, U.S. Pat. No. 4,584,125 proposes a similar dispersion of certain diorganopolysiloxanes with amine compounds, such as aniline, along with a non-aqueous dispersion agent, such as liquid petroleum and a foam destabilizing composition. Here again, this composition is not useful as an antifoam for a medical element, especially in view of the use of liquid petroleum.
As can be seen from the above, the approaches of the prior art are based on, generally speaking, combinations of a silicone oil (sometimes very specific silicone oils), some type of emulsifier, sometimes a thickening agent, such as carboxymethyl cellulose and, of course, water. As noted above, while these dispersions are applicable to a wide range of uses, including food grade uses, they are not applicable to medical substrates, such as a defoaming element in blood handling apparatus. It would, therefore, be of substantial advantage in the art to provide a dispersion of antifoam silicone oils which do not include ingredients unacceptable for application to medical substrates.